Low-temperature sinterable ceramic composition

ABSTRACT

A low-temperature sinterable ceramic composition comprising 1 to 20% by weight of Al 2  O 3 , 15 to 50% by weight of SiO 2 , 0 to 5% by weight of MgO, 3 to 18% by weight of CaO, 0 to 5% by weight of TiO 2 , 1 to 8% by weight of B 2  O 3 , 0 to 2% by weight of Li 2  O, 20 to 80% by weight of at least one of zircon, mullite and spinnel, and 1 to 12% by weight of a fluoride selected from CaF 2 , MgF 2 , LiF, AlF 3 , MnF 2 , BaF 2  and SrF 2 .

FIELD OF THE INVENTION

This invention relates to a ceramic composition which can be used as an electrically insulating material in IC packages, IC boards, multilayer wiring boards, etc., and particularly to a ceramic composition that can be sintered at low temperatures.

BACKGROUND OF THE INVENTION

Alumina having an excellent insulating property, heat resistance and mechanical strength has been widely used as an electrically insulating material. However, the sintering temperature of alumina is 1300° to 1600° C. This high firing temperature leads to a high cost of production.

In addition, boards, etc. have been made of high-melting metals, such as W and Mo-Mn as a conductive material. However, such conductive metals have high electrical resistance, and therefore, the speed of transmitting signals is slow.

In Japanese Patent Application Nos. 27124/1985 and 27125/1985, ceramic materials which can be fired at temperatures of not higher than 1,000° C. and on which a low-electric resistance conductor such as Ag, Ag-Pd, Au and Cu, can be attached and baked were studied. The results of these studies yielded a material composed of SiO₂ -CaO-Al₂ O₃ -B₂ O₃ and zircon and a material composed of (SiO₂ -CaO-B₂ O₃ -Al₂ O₃), respectively.

Crystallized glass has a relatively high mechanical strength as a material onto which a low-electric resistance metal is baked, but is of high cost. A sintered ceramic body is inexpensive, but has the disadvantage of low strength. The ceramic compositions described in the above-cited Japanese Patent applications are improved to some extent, but it is desired to develop a more improved ceramic composition.

SUMMARY OF THE INVENTION

It has been found in the present invention that a ceramic composition comprising a fluoride meets the aforesaid requirements. Specifically, the present invention relates to a low-temperature sinterable ceramic composition comprising 1 to 20% by weight of Al₂ O₃, 15 to 50% by weight of SiO₂, 0 to 5% by weight of MgO, 3 to 18% by weight of CaO, 0 to 5% by weight of TiO₂, 1 to 8% by weight of B₂ O₃, 0 to 2% by weight of Li₂ O, 20 to 80% by weight of at least one of zircon, mullite and spinel, and 1 to 12% by weight of a fluoride selected from CaF₂, MgF₂, LiF, AlF₃, MnF₂, BaF₂ and SrF₂.

DETAILED DESCRIPTION OF THE INVENTION

When the amount of Al₂ O₃ is less than 1% by weight, the coefficient of thermal expansion of the composition tends to become high. If the amount of Al₂ O₃ exceeds 20% by weight, the sintering temperature of the composition tends to become high. If the amount of SiO₂ is less than 15% by weight, the resulting composition tends to have a high sintering temperature and a high dielectric constant. If it exceeds 50% by weight, the coefficient of thermal expansion of the composition tends to increase. If the amount of MgO is larger than 5% by weight, the composition tends to have a high sintering temperature and a high coefficient of thermal expansion. If the amount of CaO is less than 3% by weight, the sintering temperature of the composition tends to become high, and if the amount of CaO is larger than 18% by weight, the dielectric constant of the composition tends to be high. If the amount of TiO₂ is larger than 5% by weight, the resulting composition tends to have a high dielectric constant. If the amount of B₂ O₃ is less than 1% by weight, the composition tends to have a high sintering temperature, and if it exceeds 8% by weight, the composition tends to have a low impact strength. If the amount of Li₂ O is larger than 2% by weight, the impact strength of the composition tends to become low. If the amount of zircon, mullite or spinel is less than 20% by weight, the resulting composition tends to have low impact strength and a high coefficient of thermal expansion. If the amount of any of these components exceeds 80% by weight the sintering temperature of the composition tends to become too high. In particular, if zircon is used as a ingredient, the dielectric constant of the composition also tends to become high. If the amount of the fluoride is less than 1% by weight, the flexural strength of the composition tends to become low, and if it is larger than 12% by weight, the coefficient of thermal expansion of the composition tends to become too high.

The zircon, mullite and spinel are natural occuring products which are of more than 99% by weight in purity and have compositions of ZrO₂.SiO₂, 3Al₂ O₃.2SiO₂ and MgO.Al₂ O₃ respectively. These may contain less than 0.1% by weight of total amount of Na₂ O and K₂ O as impurities.

The most preferable composition according to the present invention comprises 2 to 4% by weight of Al₂ O₃, 20 to 40% by weight of SiO₂, 0.5 to 1% by weight of MgO, 5 to 10% by weight of CaO, 1 to 2% by weight of TiO₂, 3 to 6% by weight of B₂ O₃, 0.5 to 1% by weight of Li₂ O, 40 to 60% by weight of zircon and 4 to 8% by weight of CaF₂ or SrF₂.

One difference between the composition of this invention and that of the prior art is that the fluoride is incorporated in the composition. This can markedly increase the mechanical strength of the resulting composition, and at the same time, decrease the firing temperature of the ceramic composition. The details of the action of the fluoride, however, have not yet been elucidated.

The ceramic composition according to the present invention may be molded in a usual manner, such as press molding, sheet molding, etc, and sintered. For example, in a press molding, an aqueous mixture of raw material of the composition and binder is mixed and ground, for example, in a ball-mill, dried by spray dry, freeze dry etc., sieved and pressed to obtain a molded product.

In the process, polyvinylalcohol (PVA), carboxymethyl cellulose (CMC), methyl cellulose (MC), acryl emulsion and gum arabic may be used in an amount of 1 to 5% by weight based on a dry raw material as 100.

In a sheet molding, a raw material is dispersed in a dispersant, such as toluene, ketone, etc. together with a binder, such as acrylic resin, butyral resin, etc., and a plasticizer, such as polyethylene glycohol, phthalate ester, etc., kneaded and ground, reduced form, tape casted, dried, and degreased to obtain molded product. In this process 20 to 30% by weight of the binder and 5 to 10% by weight of the plasticizer based on a dry raw material as 100, may be used.

The present invention is further explained in detail with referring to the following non-limiting examples.

EXAMPLE

    ______________________________________                                         Alumina (Al.sub.2 O.sub.3)                                                     Silicic anhydride (SiO.sub.2 reagent)                                                                      500 g                                              Magnesium oxide MgO reagent)                                                                               (the proportions                                   Calcium carbonate (CaCO.sub.3 reagent)                                                                     of the in-                                         Titanium dioxide (TiO.sub.2 reagent)                                                                       dividual com-                                      Boron oxide (B.sub.2 O.sub.3 reagent)                                                                      ponents are                                        Lithium meta-silicate (Li.sub.2 SiO.sub.3 reagent)                                                         indicated in                                       At least one of zirconium, mullite                                                                         the following                                      and spinel                  tables)                                            Fluoride                                                                       Hydroxypropyl cellulose (HPC-SL,                                                                           15 g                                               a tradename for a product of                                                   Nippon Soda Co., Ltd.                                                          Water                       400 ml                                             ______________________________________                                    

The above component were put in a 3-liter alumina ceramic ball mill together with 2 kg of alumina ceramic spheres having a diameter of 15 mm, and mixed at 84 rpm for 50 hours.

The resulting slurry was lyophilized by a lyophilizer for 15 hours. The dried powder was passed through a 32-mesh sieve and then compressed in a mold into a desired shape under a pressure of 1500 kg/cm². The molded product was examined for its sintering temperature, fluxural strength, dielectric constant, and coefficient of thermal expansion. The results are shown below.

    __________________________________________________________________________                                                     Dielec-  Coeffi-                                                     Sinter-   tric                                                                               Dielec-                                                                             cient of                                           Zircon   ing       Con-                                                                               tric Thermal                                            or       Temper-                                                                             Flexural                                                                            stant                                                                              Power                                                                               Ex-                   Sample                       Mullite,                                                                            Fluo-                                                                              ature                                                                               Strength                                                                            at  Factor                                                                              pansion               No.    Al.sub.2 O.sub.3                                                                   SiO.sub.2                                                                         MgO                                                                               CaO                                                                               TiO.sub.2                                                                         B.sub.2 O.sub.3                                                                   Li.sub.2 O                                                                        Spinel                                                                              ride                                                                               °C.                                                                          kg/cm.sup.2                                                                         1 MHz                                                                              × 10.sup.-4                                                                   × 10.sup.-6                                                               /°C.          __________________________________________________________________________      1     5   26.25                                                                             1.0                                                                               10.5                                                                              1.5                                                                               5.0                                                                               0.75                                                                              Zr 50                                                                               0   950  2030 7.4 34   7.2                   Comparison                                                                      2     4.95                                                                               25.99                                                                             0.99                                                                              10.40                                                                             1.49                                                                              4.95                                                                              0.74                                                                              Zr 49.5                                                                             CaF.sub.2                                                                          930  2160 7.3 35   7.3                   Invention                         1                                             3     4.75                                                                               24.94                                                                             0.95                                                                              9.98                                                                              1.43                                                                              4.75                                                                              0.71                                                                              Zr 47.5                                                                             CaF.sub.2                                                                          910  2460 7.1 39   7.5                   Invention                         5                                             4     4.4 23.1                                                                              0.88                                                                              9.24                                                                              1.32                                                                              4.4                                                                               0.66                                                                              Zr 44.0                                                                             CaF.sub.2                                                                          900  2650 7.0 46   7.7                   Invention                         12                                            5     4.25                                                                               22.31                                                                             0.85                                                                              8.93                                                                              1.28                                                                              4.25                                                                              0.64                                                                              Zr 42.5                                                                             CaF.sub.2                                                                          880  2670 6.8 53   8.2                   Comparison                        15                                            6     4.75                                                                               24.94                                                                             0.95                                                                              9.98                                                                              1.43                                                                              4.75                                                                              0.71                                                                              Zr 47.5                                                                             MgF.sub.2                                                                          910  2430 7.1 40   7.6                   Invention                         5                                             7     4.75                                                                               24.94                                                                             0.95                                                                              9.98                                                                              1.43                                                                              4.75                                                                              0.71                                                                              Zr 47.5                                                                             AlF.sub.3                                                                          920  2410 7.2 36   7.5                   Invention                         5                                             8     4.75                                                                               24.94                                                                             0.95                                                                              9.98                                                                              1.43                                                                              4.75                                                                              0.71                                                                              Zr 47.5                                                                             LiF 910  2450 7.0 39   7.6                   Invention                         5                                             9     7.24                                                                               38.00                                                                             1.45                                                                              15.21                                                                             2.18                                                                              7.24                                                                              1.08                                                                              Zr 20                                                                               CaF.sub.2                                                                          880  2130 6.8 41   7.7                   Invention                         7.62                                         10     1.81                                                                               9.50                                                                              0.36                                                                              3.80                                                                              0.54                                                                              1.81                                                                              8.27                                                                              Zr 80                                                                               CaF.sub.2                                                                          960  2400 7.8 28   6.6                                                     1.90                                         11     4.75                                                                               24.94                                                                             0.95                                                                              9.98                                                                              1.43                                                                              4.75                                                                              0.71                                                                              Spinel                                                                              CaF.sub.2                                                                          915  2530 7.2 30   8.6                                                47.5 5                                            12     4.75                                                                               24.94                                                                             0.95                                                                              9.98                                                                              1.43                                                                              4.75                                                                              0.71                                                                              Mullite                                                                             CaF.sub.2                                                                          920  2410 6.6 41   7.6                   Invention                    47.5 5                                            13     4.75                                                                               24.94                                                                             0.95                                                                              9.98                                                                              1.43                                                                              4.75                                                                              0.71                                                                              Spinel                                                                              CaF.sub.2                                                                          900  2490 7.0 29   7.8                   Invention                    47.5 5                                            14     1   25.92                                                                             0.99                                                                              10.37                                                                             1.49                                                                              4.94                                                                              0.74                                                                              Zr 49.4                                                                             CaF.sub.2                                                                          900  2460 7.0 40   7.9                   Invention                         5.20                                         15     20  20.95                                                                             0.80                                                                              8.38                                                                              1.20                                                                              3.99                                                                              0.60                                                                              Zr 39.9                                                                             CaF.sub.2                                                                          990  2480 7.8 31   7.2                   Invention                         4.20                                         16     5.38                                                                               15 1.08                                                                              11.30                                                                             1.62                                                                              5.38                                                                              0.80                                                                              Zr 53.79                                                                            CaF.sub.2                                                                          980  2420 7.9 40   7.0                   Invention                         5.66                                         17     3.16                                                                               50 0.63                                                                              6.65                                                                              0.95                                                                              3.16                                                                              0.47                                                                              Zr 31.64                                                                            CaF.sub.2                                                                          890  2420 6.8 41   8.2                   Invention                         3.33                                         18     4.80                                                                               25.18                                                                             0  10.08                                                                             1.44                                                                              4.80                                                                              0.72                                                                              Zr 47.96                                                                            CaF.sub.2                                                                          900  2440 7.0 40   7.3                   Invention                         5.05                                         19     4.56                                                                               23.92                                                                             5  9.57                                                                              1.37                                                                              4.56                                                                              0.68                                                                              Zr 45.56                                                                            CaF.sub.2                                                                          990  2430 7.1 40   7.8                   Invention                         4.80                                         20     5.12                                                                               26.87                                                                             1.01                                                                              3  1.54                                                                              5.12                                                                              0.77                                                                              Zr 51.18                                                                            CaF.sub.2                                                                          980  2450 6.9 38   7.2                   Invention                         5.39                                         21     4.33                                                                               22.72                                                                             0.87                                                                              18 1.30                                                                              4.33                                                                              0.65                                                                              Zr 43.27                                                                            CaF.sub.2                                                                          880  2470 7.8 40   7.8                   Invention                         4.55                                         22     4.82                                                                               25.30                                                                             0.96                                                                              10.12                                                                             0  4.82                                                                              0.72                                                                              Zr 48.19                                                                            CaF.sub.2                                                                          940  2380 6.7 37   7.3                   Invention                         5.07                                         23     4.58                                                                               24.04                                                                             0.92                                                                              9.62                                                                              5  4.58                                                                              0.68                                                                              Zr 45.78                                                                            CaF.sub.2                                                                          870  2510 7.9 43   7.6                   Invention                         4.82                                         24     4.94                                                                               25.92                                                                             0.99                                                                              10.37                                                                             1.49                                                                              1  0.74                                                                              Zr 49.37                                                                            CaF.sub.2                                                                          1000 2480 7.0 38   7.6                   Invention                         5.20                                         25     4.59                                                                               24.09                                                                             0.92                                                                              9.64                                                                              1.38                                                                              8  0.69                                                                              Zr 45.88                                                                            CaF.sub.2                                                                          840  2030 7.2 41   7.2                   Invention                         4.83                                         26     4.78                                                                               25.12                                                                             0.96                                                                              10.05                                                                             1.44                                                                              4.78                                                                              0  Zr 47.84                                                                            CaF.sub.2                                                                          940  2450 7.3 38   7.6                   Invention                         5.04                                         27     4.69                                                                               24.62                                                                             0.94                                                                              9.85                                                                              1.41                                                                              5.69                                                                              2  46.88                                                                               CaF.sub.2                                                                          870  2110 6.8 40   7.4                                                     4.94                                         28     4.75                                                                               24.94                                                                             0.95                                                                              9.98                                                                              1.43                                                                              4.75                                                                              0.71                                                                              Zr 23.75                                                                            CaF.sub.2                                                                          910  2480 7.1 35   7.6                   Invention                    Spinel                                                                              5                                                                         23.75                                             29     4.75                                                                               24.94                                                                             0.95                                                                              9.98                                                                              1.43                                                                              4.75                                                                              0.71                                                                              Zr 23.75                                                                            CaF.sub.2                                                                          920  2430 6.9 40   7.4                   Invention                    Spinel                                                                              5                                                                         23.75                                             30     4.75                                                                               24.94                                                                             0.95                                                                              9.98                                                                              1.43                                                                              4.75                                                                              0.71                                                                              Zr 23.75                                                                            CaF.sub.2                                                                          910  2460 6.8 36   7.6                   Invention                    Spinel                                                                              5                                                                         23.75                                             __________________________________________________________________________

Since the ceramic composition has a sintering temperature of not more than 1000° C., the cost of firing can be curtailed, and low-resistance conductors such as Ag, Ag-Pd, Au and Cu can be baked on it. As a result, the speed of transmitting signals can be increased. Furthermore, the ceramic composition of this invention has a flexural strength of as high as about 2,000 to 2,500 kg/cm² and a sufficiently low dielectric constant and dielectric power factor. In addition, its coefficient of thermal expansion is not high.

It is preferred in the present invention that the low-temperature sinterable ceramic composition has a sintering temperature of not higher than 1,000° C., a flexural strength of at least 2,100 kg/cm², a dielectric constant of not more than 8 at 1 MHz and a coefficient of thermal expansion of not more than 8×2⁻⁶ /°C., more preferably a stintering temperature of 850° to 950° C., a flexural strength of at least 2,500 kg/cm², a dielectric constant of not more than 6 at 1 MHz and coefficient of thermal expansion of not more than 4 to 6×10⁻⁶ /°C.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. 

What is claimed is:
 1. A low-temperature sinterable ceramic composition consisting essentially of 1 to 20% by weight of Al₂ O₃, 15 to 50% by weight of SiO₂, 0 to 5% by weight of MgO, 3 to 18% by weight of CaO, 0 to 5% by weight of TiO₂, 1 to 8% by weight of B₂ O₃, 0 to 2% by weight of Li₂ O, 20 to 80% by weight of at least one zircon, mullite and spinel, and 1 to 12% by weight of a fluoride selected from CaF₂, MgF₂, LiF, AlF₃, MnF₂ and SrF₂, wherein said composition has a sintering temperature of not more than 1,000° C., a flexural strength of at least 2,100 kg/cm², a dielectric constant of not more than 8 at 1 MHz, and a coefficient of thermal expansion of not more than 8×10⁻⁶ /°C.
 2. A low-temperature sinterable ceramic composition of claim 1, wherein the composition consists essentially of 2 to 4% by weight of Al₂ O₃, 20 to 40% by weight of SiO₂, 0.5 to 1% by weight of MgO, 5 to 10% by weight of CaO, 1 to 2% by weight of TiO₂, 3 to 6% by weight of B₂ O₃, 0.5 to 1% by weight of Li₂ O, 40 to 60% by weight of Zircon and 4 to 8% by weight of CaF₂ or SrF₂. 